1. Field of the Invention
The present invention generally relates to a motor, in particular to a brushless motor having a stator on which an insulator is arranged.
2. Background of the Related Art
Conventionally, a brushless motor (hereinafter simply referred to as a motor) used for an electric powered power-steering system includes a bus bar having a connector to which a coil arranged on a stator is connected. The stator is centered on a center axis and is formed by axially laminating a plurality of steel plates. The stator includes a core back having a circular shape centered on the center axis and teeth extending radially inwardly from an inner circular surface of the core back. The teeth are arranged in a circumferentially spaced manner from each other. A set of insulators, each of which has a U-shape, are attached to each of the teeth. One of the insulators is attached to each of the teeth from an axially upper side thereof, and the other is attached to the teeth from an axially lower side thereof. Then, a wire is wound around each of the teeth via the insulators such that a coil defined by a multilayer structure of the wire on the teeth is provided on each of the teeth.
Recently, there has been a demand for reducing vibration of the motor used for the powered steering system in order to realize smooth steering. One way to meet the demand is increasing the number of teeth of the stator.
In addition, a number of turns of the wires wound around the teeth may be increased to reduce a space between adjacent teeth (i.e., increase a packing factor of the coils). In order to increase the packing factor and number of teeth, a technique described below has been introduced. Conventionally, a plurality of stator cores, each of which has a tooth, respectively, are separately formed, and a coil is formed on each of the teeth. Then, stator cores are circumferentially attached to each other to provide a stator. Such technique is simply referred to as a divided-core-manufacturing method. In another example, the coils are formed on each of the teeth extending from the core back which has a substantially linear shape, then, the core back is bent at predetermined positions so as to form the circular shape. Such technique is simply referred to as a curving-core-manufacturing method.
In the above-described technique, the wire may be wound around each of the teeth separately, and thus, each of the teeth may include two wire-ends, a winding-starting end and a winding-terminating end. Thus, the bus bar includes twice as many terminals as the number of the teeth.
As number of the terminals arranged on the bus bar increases, space between each terminals is reduced. With a reduced space between adjacent terminals, it becomes difficult to connect the wires to the terminals. In particular, the wire used in the motor for the power steering system generally has a thick dimension. Thus, in the view of workability of connecting wires, it is preferable that the space between adjacent terminals is sufficiently wide.
It is demanded that a component of a vehicle has high reliability under various circumstances for extended periods of time. Thus, it is required that the motor used for the power steering system have that property.